Creates a `fixedBuffer` type that is used to encapsulate functionality
for reading/writing from the underlying byte slices.
Uses lazily-loaded set of sync.Pools for storing buffers that are no
longer needed so they can be re-used.
```
benchmark old ns/op new ns/op delta
BenchmarkBytesPipeWrite-8 138469 48985 -64.62%
BenchmarkBytesPipeRead-8 130922 56601 -56.77%
benchmark old allocs new allocs delta
BenchmarkBytesPipeWrite-8 18 8 -55.56%
BenchmarkBytesPipeRead-8 0 0 +0.00%
benchmark old bytes new bytes delta
BenchmarkBytesPipeWrite-8 66903 1649 -97.54%
BenchmarkBytesPipeRead-8 0 1 +Inf%
```
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
